Corrosion-resistant, chromium-free, self-priming coatings curable by ultraviolet light

ABSTRACT

Corrosion-resistant, self-priming coatings that are curable by ultraviolet energy and methods for coating surfaces using such coatings have been provided. In an exemplary embodiment, a method for coating a surface includes formulating a chromium-free, self-priming coating, applying the chromium-free, self-priming coating to the surface, and curing the chromium-free, self-priming coating with ultraviolet light.

TECHNICAL FIELD

The embodiments described herein generally relate to protectivecoatings, and more particularly relate to corrosion-resistant,chromium-free, self-priming coatings that are curable by ultravioletlight and methods for painting surfaces, particularly aircraft andspacecraft, using ultraviolet light-curable, corrosion-resistant,chromium-free, self-priming coatings.

BACKGROUND

Aircraft utilize a protective coating system that is applied to theaircraft to minimize corrosion and resistance of the exterior surface ofan aircraft and to provide the desired color, infrared properties,impact resistance, and gloss to the exterior surface. Current protectivecoating systems often consist of a primer and a separate topcoat film,both individually applied to the aircraft. Primer coatings that meetcurrent military specifications typically are epoxy resins pigmentedwith strontium chromate for corrosion protection. Topcoats that meetcurrent military specifications typically are polyurethane resins withappropriate pigmentation to provide color, infrared properties, and lowgloss.

However, such protective coating systems suffer from several distinctdrawbacks. Corrosion inhibitors containing chromium (VI) compounds, suchas strontium chromate, are widely and effectively used to controlcorrosion of aluminum alloys, such as those used to make militaryaircraft. However, while these chromium compounds have excellentcorrosion protective and inhibitive properties, they are toxic andsuspected carcinogens. Compliance with current environmental, safety andhealth regulations relating to chromium use is expensive. As trends toincrease the stringency of occupational health and environmentalregulations continue, the use of chromium may no longer be feasible.

In addition, high performance coating systems typically contain volatileorganic compounds (VOCs), which result in the production of smog, andhazardous air pollutants (HAPs) such as methyl ethyl ketone (MEK),toluene, and xylene. Standards for emissions continue to becomestricter. Accordingly, the indefinite continuation of current technologyutilizing compounds that release VOCs and HAPs is not only undesirable,but may not be possible in the future.

The above-described coatings also are logistically and operationallyundesirable. A key area of concern in the aerospace/military industry iscycle time reduction for systems applications. It is also desirable forcoating systems to be easily and quickly repairable in the event ofdamage. However, the current coating systems require the application oftwo separate coatings, the primer and the topcoat. In addition, thecuring time for current aerospace/military coatings can be as long as 72hours or more, significantly reducing the operation availability of theaircraft.

Accordingly, it is desirable to provide a protective corrosion-resistantcoating for military and commercial aircraft and spacecraft that doesnot utilize chromium or chromium compounds and that releases minimal orno VOCs or HAPs. In addition, it is desirable to provide a protectivecoating for military and commercial aircraft and spacecraft that can beapplied and cured quickly. It is also desirable to provide a method forpainting an aircraft with such a protective coating system. Furthermore,other desirable features and characteristics of the chrome-free,self-priming coating will become apparent from the subsequent detaileddescription and the appended claims, taken in conjunction with theaccompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

In an exemplary embodiment, a method for coating a surface comprises thesteps of formulating a chromium-free, self-priming coating, applying thechromium-free, self-priming coating to the surface, and curing thechromium-free, self-priming coating with ultraviolet light.

In another exemplary embodiment, a coating for a surface comprises: anacrylated oligomer selected from the group consisting of acrylates,methacrylates, diacrylates, triacrylates, and polyacrylates; a monomerselected from the group consisting of acrylates, methacrylates,diacrylates, triacrylates, polyacrylates, allyl compounds, vinyl ethers,vinyl esters, vinyl carboxylic acids, vinyl carboxylic acid salts, vinylamides, unsaturated dicarboxylic acids, and derivatives thereof, aphotoinitiator; and a chromium-free corrosion inhibitor.

In a further exemplary embodiment, a method for coating a surfacecomprises combining to form a single mixture an acrylated oligomerselected from the group consisting of acrylates, methacrylates,diacrylates, triacrylates, and other polyacrylates, a monomer selectedfrom the group consisting of acrylates, methacrylates, diacrylates,triacrylates, polyacrylates, allyl compounds, vinyl ethers, vinylesters, vinyl carboxylic acids, vinyl carboxylic acid salts, vinylamides, unsaturated dicarboxylic acids, and derivatives thereof, aphotoinitiator, a chromium-free corrosion inhibitor, and a pigment. Themixture is applied to the surface and is exposed to ultraviolet light.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is a flowchart of a method for coating a surface with aprotective coating, in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the described embodiments or the application anduses of the described embodiments. Furthermore, there is no intention tobe bound by any expressed or implied theory presented in the precedingtechnical field, background, brief summary or the following detaileddescription.

A protective coating, in accordance with an exemplary embodiment,comprises an oligomer, a monomer, a photoinitiator, and a corrosioninhibitor such that the protective coating provides corrosionresistance, is free of chromium, and releases minimal or no VOCs andHAPs. The coating is cured by ultraviolet (UV) light and is applied to asurface as a “self-priming” coating. As used herein, a “self-priming”coating means a single coating, or a coating that can be applied in asingle application, that contains a corrosion inhibitor, typically foundin primer coatings, with oligomers and monomers that generally determinethe physical properties of a topcoat, such as weatherability andviscosity. Accordingly, the UV-curable, self-priming coating decreasesmanufacturing cycle times and thus decreases the amount of time anaircraft is operationally unavailable. While the protective coating isdescribed herein for use on military and commercial aircraft andspacecraft, it will be understood that the protective coating is not solimited, and may be used on trains, in marine ship applications,automotive applications, and other vehicle and industrial applications.

The oligomer of the protective coating generally determines the physicalproperties and characteristics of the protective coating. In oneexemplary embodiment, oligomers useful for formulating the protectivecoating include acrylated oligomers selected from the group consistingof acrylates, methacrylates, diacrylates, triacrylates, and otherpolyacrylates. As used herein, the term “acrylates” is used generally toinclude derivatives of acrylic acid as well as derivatives ofsubstituted acids, such as, for example, methacrylic acid, ethacrylicacid, and the like, unless clearly indicated otherwise, and thereforeencompasses methacrylates, ethacrylates, etc. Examples of acrylatedoligomers include aliphatic polyether urethane acrylates, diacrylates,triacrylates, and polyacrylates; aliphatic polyester urethane acrylates,diacrylates, triacrylates, and polyacrylates; aromatic polyetherurethane acrylates, diacrylates, triacrylates, and polyacrylates;aromatic polyester urethane acrylates, diacrylates, triacrylates, andpolyacrylates; polyester acrylates, diacrylates, triacrylates, andpolyacrylates; polyether acrylates, diacrylates, triacrylates, andpolyacrylates; epoxy acrylates, diacrylates, triacrylates, andpolyacrylates; polyamine acrylates, diacrylates, triacrylates, andpolyacrylates; and acrylated acrylic oligomers. Aliphatic polyetherurethane acrylates, diacrylates, and triacrylates, and aliphaticpolyester urethane acrylates, diacrylates, and triacrylates arepreferred for their flexibility and weather-resistant properties. Anexample of an aliphatic urethane diacrylate is Photomer® 6230 and anexample of an aliphatic urethane triacrylate oligomer is Photomer® 6892,both available from Cognis Corp. of Cincinnati, Ohio. Another example ofan aliphatic urethane diacrylate oligomer is CN991 and an example of analiphatic urethane diacrylate oligomer blended with 25% isobomylacrylate is CN966J75, both available from Sartomer Company, Inc. ofExton, Pa.

The monomer of the protective coating generally influences the viscosityand cure speed of the coating, as well as physical properties andcharacteristics. Monomers useful for formulating the protective coatinginclude acrylates, methacrylates, diacrylates, triacrylates,polyacrylates, allyl compounds, vinyl ethers, vinyl esters, vinylcarboxylic acids, vinyl carboxylic acid salts, vinyl amides, andunsaturated dicarboxylic acids, and derivatives thereof.

Examples of acrylate monomers which can be utilized in the protectivecoating include, but are not limited to, one or more of the following:ethylhexyl acrylate, 2-ethoxyethyl acrylate, cyclohexyl acrylate, laurylacrylate, stearyl acrylate, such as SR 257 available from SartomerCompany, Inc. of Exton, Pa., alkoxylated phenol acrylates, alkoxylatednonylphenol acrylates, nonylphenol acrylate, isobomyl acrylate, such asSR506D available from Sartomer Company, Inc., acrylated epoxy soya oil,acrylated epoxy linseed oil, caprolactone acrylate, 2-phenoxyethylacrylate, benzyl acrylate, monomethoxy tripropylene glycol monoacrylate,monomethoxy neopentyl glycol propoxylate monoacrylate, 1,3-butanedioldiacrylate, 1,4-butanediol diacrylate, 1,6-hexanedioldiacrylate,1,8-octanediol diacrylate, 1,10-decanediol diacrylate, polybutadienediacrylate, trimethylolpropane triacrylate, glyceryl triacrylate,pentaerythritol triacrylate, pentaerythritoltetraacrylate,dipentaerythritol pentaacrylate, di-trimethylolpropane tetraacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate, tetrahydrofurfurylacrylate, isooctyl acrylate, isodecyl acrylate, such as SR 395 availablefrom Sartomer Company, Inc., 2-(2-ethoxyethoxy) ethyl acrylate, ethyleneglycol diacrylate, propylene glycol diacrylate, neopentyl glycoldiacrylate, cyclopentenyl oxyethyl acrylate, 9-anthracenyl methylacrylate, 1-pyrenylmethyl acrylate, and Fluorescein diacrylate. As usedherein, the terms “acrylic” and “acrylate” should be defined generallyto include derivatives of acrylic acids as well as substituted acrylicacids such as methacrylic acid, ethacrylic acid, etc., with alkyl chainsof 1 to 8 carbon atoms, unless clearly indicated otherwise. Alsoincluded are acrylate/methacrylate combinations and mixtures. Forinstance, the above listing therefore is understood to includemethacrylate monomers including, but not limited to, one or more of thefollowing: ethylhexyl methacrylate, 2-ethoxyethyl methacrylate,cyclohexyl methacrylate, lauryl methacrylate, stearyl methacrylate, suchas SR 324 available from Sartomer Company, Inc., alkoxylated phenolmethacrylates, alkoxylated nonylphenol methacrylates, nonylphenolmethacrylate, isobomyl methacrylate, methacrylated epoxy soya oil,methacrylated epoxy linseed oil, caprolactone methacrylate,2-phenoxyethyl methacrylate, benzyl methacrylate, monomethoxytripropylene glycol monomethacrylate, monomethoxy neopentyl glycolpropoxylate monomethacrylate, 1,3-butanediol dimethacrylate,1,4-butanediol dimethacrylate, 1,6-hexanedioldimethacrylate,1,8-octanediol dimethacrylate, 1,10-decanediol dimethacrylate,polybutadiene dimethacrylate, trimethylolpropane trimethacrylate,glyceryl trimethacrylate, pentaerythritol trimethacrylate,pentaerythritoltetramethacrylate, dipentaerythritol pentamethacrylate,di-trimethylolpropane tetramethacrylate,tris(2-hydroxyethyl)isocyanurate trimethacrylate, tetrahydrofurfurylmethacrylate, isooctyl methacrylate, isodecyl methacrylate,2-(2-ethoxyethoxy) ethyl methacrylate, ethylene glycol dimethacrylate,propylene glycol dimethacrylate, neopentyl glycol dimethacrylate,cyclopentenyl oxyethyl methacrylate, 9-anthracenyl methyl methacrylate,1-pyrenylmethyl methacrylate, Fluorescein dimethacrylate, andacrylate/methacrylate combinations.

Examples of monomers that can be utilized in the protective coating alsoinclude, but are not limited to, one or more of the following acrylatecompounds containing alkoxy units, as well as the correspondingmethacrylates, higher alkyl acrylates, and mixtures thereof: diethyleneglycol diacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, dipropylene glycoldiacrylate, tripropylene glycol diacrylate, tetrapropylene glycoldiacrylate, polypropylene glycol diacrylate, glyceryl ethoxylatediacrylate, glyceryl propoxylate diacrylate, glyceryl ethoxylatetriacrylate, glyceryl propoxylate triacrylate, trimethylolpropaneethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, suchas SR492 available from Sartomer Company, Inc., neopentylglycolethoxylate diacrylate, neopentylglycol propoxylate diacrylate,monomethoxy trimethylolpropane ethoxylate diacrylate, monomethoxytrimethylolpropane propoxylate diacrylate, pentaerythritol ethoxylatetetraacrylate, such as SR494 available from Sartomer Company, Inc.,pentaerythritol propoxylate tetraacrylate, dipentaerythritol ethoxylatepentaacrylate, dipentaerythritol propoxylate pentaacrylate,di-trimethylolpropane ethoxylate tetraacrylate, di-trimethylolpropanepropoxylate tetraacrylate, Bisphenol A ethoxylate diacrylate, andBisphenol A propoxylate diacrylate.

Examples of allyl compounds that can be utilized in the protectivecoating include, but are not limited to, allyl propoxylate, allylcinnamate (allyl 3-phenylacrylate) available from Sigma-Aldrich Companyof St. Louis, Mo., diallyl phthalate, tripropyleneglycol diallyl ether,pentaerythritol allyl ether, trimethylolpropane diallyl ether,trimethylolpropane monoallyl ether, triallyl cyanurate, triallylisocyanurate, and hydroxy terminated ethyleneglycolbis[pentakis(glycidyl allyl ether)]ether. The monomers also may containmore than one type of reactive group, for example allyl methacrylate,ethoxylated allyl methacrylate, propoxylated allyl methacrylate, anddi(propyleneglycol) allyl ether methacrylate.

Examples of vinyl ethers which can be utilized in the protective coatinginclude, but are not limited to, ethyl vinyl ether, butyl vinyl ether,hydroxy butyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinylether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether,octadecyl vinyl ether, cyclohexane dimethanol monovinyl ether, phenylvinyl ether, 1,6-hexanediol divinyl ether, 1,4-cyclohexane dimethanoldivinyl ether, diethylene glycol divinyl ether, triethylene glycoldivinyl ether, tetraethylene glycol divinyl ether, dipropylene glycoldivinyl ether, tripropylene glycol divinyl ether, tetrapropylene glycoldivinyl ether, and the propenyl ether of propylene carbonate. Examplesof vinyl esters include vinyl propionate, vinyl acetate, and vinyl2-ethyl hexanoate.

The protective coating is curable by UV light and generally contains atleast one photoinitiator. Photoinitiators absorb UV radiation andgenerate species that initiate polymerization. Photoinitiators may beclassified in two major groups based upon a mode of action.Cleavage-type photoinitiators include acetophenones, benzoin ethers,benzoyl oximes, and acyl phosphines. Abstraction-type photoinitiatorsinclude benzophenone, Michler's ketone, thioxanthones, anthraquinone,camphorquinone and ketocoumarin. Abstraction-type photoinitiatorsfunction better in the presence of materials such as amines and otherhydrogen donor materials added to provide labile hydrogen atoms forabstraction. In the absence of such added materials, photoinitiation maystill occur via hydrogen abstraction from monomers, oligomers, or othercomponents of the system.

Examples of photoinitiators that may be used include, but are notlimited to, one or more of the following: benzophenone, benzyldimethylketal, isopropylthioxanthone, bis(2,4,6-trimethybenzoyl)phenylphosphineoxide, bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide,2-hydroxy-2-methyl-1-phenyl-1-propanone,diphenyl(2,4,6-trimethybenzoyl)phosphine oxides, 1-hydroxycyclohexylphenyl ketone,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,α,α-dimethoxy-(α-phenylacetophenone, 2,2-diethoxyacetophenone,2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, and2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone. In oneexemplary embodiment, the photoinitiator is an acylphosphine oxide dueto favorable absorption characteristics in the high wavelength region ofthe UV spectrum that are not obscured by pigment absorption. In anotherexemplary embodiment, the photoinitiator is bisacylphosphine oxide(BAPO).

Combinations of photoinitiators may be used to achieve the mostappropriate degree of through cure and surface cure of coatingcompositions for desired appearance and properties. Reactivephotoinitiators, which contain polymerizable groups, may also be used toreact the photoinitiator molecules into the polymer matrix. The cureprocess is generally more efficient in the absence of oxygen, forexample, in the presence of nitrogen, so a greater amount ofphotoinitiator is generally required in the presence of oxygen.

Examples of hydrogen donor materials that may be utilized in combinationwith photoinitiators include, but are not limited to, one or more of thefollowing: ethyl-4-dimethylaminobenzoate,octyl-p-(dimethylamino)benzoate, N-methyldiethanolamine,dimethylethanolamine, triethanolamine, tri-n-propylamine,diethylethanolamine, triethylamine, diisopropylethylamine,diisopropylethanolamine, dimethylaminomethylphenol,tris(dimethylaminomethyl)phenol, benzyldimethylamine, amine acrylates,and amine methacrylates.

In addition, the protective coating also comprises a corrosioninhibitor. Examples of corrosion inhibitors include chromium-freerare-earth inhibitors, such as Rhett P3 available from Deft, Inc. ofIrvine, Calif., Hybricor™ 204 (previously Wayncor® 204) from WaynePigment Corp. of Milwaukee, Wis., andpoly(2,5-dimercapto-1,3,4-thiadiazole (PolyDMcT) available fromCrosslink of St. Louis, Mo.

In addition to the above-described components, in an exemplaryembodiment, the protective coating may include other pigment andadditive compounds known to those of skill in the art. These compoundsmay include, but are not limited to pigments, fillers, fluorescentadditives, flow and leveling additives, wetting agents, surfactants,antifoaming agents, rheology modifies, adhesion promoters, opticalbrighteners, stabilizers, and antioxidants. Exemplary additives arethose that do not have appreciable absorption in the UV wavelengthsspectra used to cure the coating. Examples of pigments and fillermaterials include, but are not limited to, titanium dioxide, such asTi-Pure® R960 available from E. I. du Pont de Nemours and Company ofWilmington, Del. and Tioxide® TR93 available from Huntsman InternationalLLC of Salt Lake City, Utah, colloidal silica, such as Syloid® Rad 2005and Syloid® ED-30 available from Grace Davison of Columbia, Md.,hydrophilic silica, hydrophobic amorphous fumed silica, amorphousprecipitated silica, magnesium silicate, calcium carbonate, calciumsilicate, carbon black, and polymer powders.

Examples of flow and leveling additives, wetting agents, and antifoamingagents that may be used to formulate the protective coating includesilicones, modified silicones, silicone acrylates, hydrocarbons,fluorine-containing compounds, and non-silicone polymers and copolymerssuch as copolyacrylates.

Types of stabilizers that may be used to formulate the protectivecoating include hydroxyphenylbenzotriazoles, hydroxyphenyltriazines,oxalanilides, such as Sandovur® 3206 available from ClariantInternational Ltd. of Muttenz, Switzerland, hindered amine lightstabilizers (HALS), and acetylated hindered amine light stabilizers,such as Sanduvor® 3068 available from Clariant. Examples of stabilizersmay include, but are not limited to,2-(2′-hydroxy-5′-methylphenyl)-benzotriazole,2-(3′,5′-di-tert-butyl-2′-hydroxyphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)-benzotriazole, benzenepropanoicacid3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C7-9-branchedalkyl esters,2-(3′,5′-bis(1-methyl-1-phenylethyl)-2′-hydroxyphenyl)benzotriazole,2-[2-hydroxy-3-dimethylbenzylphenyl-5-(1,1,3,3-tetramethylbutyl)]-2H-benzotriazole,poly(oxy-1,2-ethanediyl)α-[3-][3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropyl]-ω-hydroxyandpoly(oxy-1,2-ethanediyl)α-[3-][3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropyl]-ω-[3-][3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]-,2-[4-[2-hydroxy-3-tridecyloxypropyl]oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazineand 2-[4-[2-hydroxy-3-dodecyloxypropyl]oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,bis(1,2,2,6,6-pentamethyl-4-piperidinyl)(3,5-di-tert-butyl-4-hydroxybenzyl)butylpropanedioate,bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate,tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methane,thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate),octadecyl 3,5-di-tert-butyl-4-hydroxyhydro-cinnamate,bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, methyl(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate,tris(2,4-di-tert-butylphenyl) phosphite, and decanedioic acidbis(2,2,6,6-tetramethyl-4-piperidinyl) ester reaction products with1,1-dimethyl-ethylhydroperoxide and octane.

The protective coating, once formulated and applied to a surface, iscured by UV light. The UV light may be provided by any suitable source,such as, for example, mercury vapor lamps, pulsed xenon lamps, LEDlamps, electroless lamps, and the like. The UV light lamp may compriseone or more of Fusion H bulbs, D bulbs, Q bulbs, V bulbs, and the like,used simultaneously or serially. In an exemplary embodiment, the coatingis cured using UV light from a Fusion V bulb followed by UV light from aFusion H bulb. Though not wishing to be bound by theory, the V bulb hasa longer wavelength that permeates the coating, thus providing moreefficient curing throughout the coating, while the H bulb has a shorterwavelength that provides a more efficient surface cure. For the highestcuring efficiency, the choice of photoinitiator or photoinitiatorcombinations, with characteristic absorbance spectra, should be matchedwith the spectral output of the bulb(s). Bulb type and intensity,exposure time, and photoinitiator choice and concentration can beadjusted to control speed of cure for a predetermined coatingappearance, with faster surface cure generally corresponding to highergloss values.

In another embodiment, the protective coating further comprisescomponents that impart a secondary cure mechanism that is active in theabsence of UV light. The secondary cure mechanism functions to improvecoating properties after the removal of UV light, and also functions toprovide coating cure in the absence of UV light, for example, in areasthat are shadowed from the UV light. Along with the primary UV cure,addition of a secondary cure mechanism results in a dual cure coating,and addition of more than one additional cure mechanism to the primaryUV cure results in a multiple cure mechanism coating. Examples ofadditional cure mechanisms that may be used for curing of the protectivecoating include free-radical cure of unsaturated compounds with aperoxide, such as cumene hydroperoxide, activated peroxide cure usingtertiary amines or metal compounds, activated cure in the absence ofperoxides using tertiary amines or metal compounds, oxidative cure ofdouble bonds in air initiated by oxygen radicals, and combinationsthereof. An example of a cumene hydroperoxide is Clear Catalyst® 11available from Sigma-Aldrich Company of St. Louis, Mo. Isocyanate curesalso may be used, although use of isocyanates may increase the amount ofVOCs and HAPs of the coating.

In one embodiment, the compositions of the protective coating may be aone-part composition in which all components of the coating can be mixedtogether in no particular sequence or order. In another embodiment, forexample in certain dual-cure or multiple-cure coating compositions, thecompositions of the protective coating may be a two-part or amultiple-part composition, with different parts of the composition mixedtogether immediately before application of the coating. For example, incompositions using an activated peroxide cure mechanism as a secondarycure mechanism, an activator may be separated from the peroxide untilimmediately before use. In a further embodiment, the monomers,activator, and peroxide are all in separate parts, with all three partsmixed together immediately before application. In compositions using anisocyanate cure as a secondary cure mechanism, the composition may be aone-part composition if the components do not contain amines,hydroxyl-containing compounds, or moisture. In exemplary embodiments, incompositions using an isocyanate cure as a secondary cure mechanism, thecomposition is at least a two-part composition, with theisocyanate-containing compound or compounds in a part separate from mostof the other components, with the separate parts mixed togetherimmediately before use.

For coating compositions using isocyanate cure as a secondary curemechanism, secondary cure components may include, but are not limitedto, at least one material having at least one isocyanate unit, and/or atleast one material having at least one acrylate unit and at least oneisocyanate unit in the same molecule. In certain embodiments, amine orhydroxyl-containing compounds may also be used to react with theisocyanate-containing material. In these embodiments, the coatingcompositions may include, but are not limited to, at least one materialcontaining at least one hydroxyl group, at least one material containingat least one amine group, at least one material containing at least onehydroxyl group and at least one acrylate unit in the same molecule, atleast one material containing at least one hydroxyl group and at leastone allyl unit in the same molecule, and/or at least one materialcontaining at least one amine group and at least one acrylate unit inthe same molecule. Examples of dual functional components containing anacrylate group and an isocyanate group include Roskydal® VP LS 2396 andRoskydal® VP LS 2337 from Bayer MaterialScience AG of Leverkusen,Germany. Isocyanate-containing polyurethane precursors andhydroxyl-containing polyurethane precursors known to those of skill inthe art may also be used along with UV curable components in the coatingcompositions of the present invention. Hydroxy-terminated polymers mayalso be used, such as hydroxy-terminated polybutadienes. An example of ahydroxyl-terminated polybutadiene for use in the protective coating isPoly bd® R20LM available from Sartomer Company, Inc. of Exton, Pa. Withthe use of hydroxyl-containing compounds, reaction with the isocyanategroups results in the formation of polyurethane linkages, and the ratioof isocyanate/hydroxyl groups can be varied to vary the properties ofthe resulting coating. In the absence of hydroxyl-containing compounds,isocyanate groups can still react through a different cure mechanism ofmoisture cure known to those of skill in the art.

In another embodiment, the composition of the protective coating maycomprise components for several different cure mechanisms. In oneembodiment, a hybrid composition may comprise components for UV cure,isocyanate cure, and oxidative cure. In another embodiment, a hybridcomposition may comprise components for UV cure, isocyanate cure, andactivated free radical cure. For example, a coating composition maycomprise at least one acrylate for UV cure, at least oneisocyanate-containing compound for moisture cure or urethane formation,and at least one allyl compound for oxidative cure.

Activator compounds may also be used to facilitate oxidative and freeradical cure. Types of activator compounds include tertiary amines andmetal compounds. Examples of activator compounds that may be used toformulate the protective coating include compounds of barium, calcium,cerium, cobalt, copper, iron, manganese, strontium, zinc, zirconium, andmixtures thereof. In an exemplary embodiment, suitable activatorcompounds comprise at least one 2-ethylhexanoic metal salt or an isomerthereof, such as Octa-Soligen® 69HS available from Borchers GmbH ofLangenfeld, Germany. Metal salts of 2-ethylhexanoic acid are also knownas metal octoates.

In accordance with an exemplary embodiment, a method 20 for coating asurface using the various embodiments of the protective coatingdescribed above is illustrated in FIG. 1. The method comprises the stepof formulating a chromium-free, self-priming coating, such as theprotective coating described above, comprising a corrosion inhibitor(step 22). The coating is formulated using one or more of the oligomers,monomers, photoinitiators, and corrosion inhibitors set forth above. Inaddition, the coating may be formulated using any of the pigments,fillers, fluorescent additives, flow and leveling additives, wettingagents, surfactants, antifoaming agents, rheology modifies, adhesionpromoters, optical brighteners, stabilizers, antioxidants, and secondaryor multiple cure mechanisms described above. The various components arethen suitably combined depending on whether the coating is a one-part,two-part, or multiple-part composition. In an exemplary embodiment,solid photoinitiators are dissolved in monomer(s) before combinationwith other components. Corrosion inhibitors may also be dispersed inoligomer(s) before combination with other components. The components canbe mixed at room temperature with stirring, shaking, agitation, and/orthe like, and heating may be employed to facilitate the mixing. If thecomponents of the composition undergo separation during storage, mildagitation or mixing prior to use may be performed to disperse thecomponents. Prior to application, as described in more detail below, allcomponents are combined by stirring, shaking agitation, and/or the like.

After formulation of the coating, the coating is applied to a surface(step 24). The coating may be applied to a surface by roller coating,brushing, spraying, or by any other means known in the art. In anexemplary embodiment, the coating may be heated or cooled to facilitatethe application process.

Following application of the coating to the surface, the coating iscured using UV energy (step 26). As described above, in variousexemplary embodiments, the photoinitiator used to formulate the coating,with characteristic absorbance spectra, is matched with the spectraloutput of the bulb that is used to provide the UV energy. The coating isexposed to the UV energy for a time sufficient to cause the coating tocure. In one exemplary embodiment of the invention, the coating isexposed to a total UV energy of about 0 to about 10 J/cm² UVA energy, incertain embodiments about 3 to about 7 J/cm² UVA energy, about 0 toabout 8 J/cm² UVB energy, in certain embodiments about 2 to about 5J/cm² UVB energy, and about 0 to about 5 J/cm² UVC energy, in certainembodiments about 0.2 to about 2 J/cm² UVC energy.

The following are examples of various compositions of the protectivecoating described above. The examples are illustrative in nature and arenot meant to limit the embodiments of the protective coating in any way.The exemplary protective coatings are single-application, self-primingcoatings that exhibit corrosion resistance, are chromium-free, andrelease minimal or no VOCs and HAPs. Unless indicated, all componentsare listed in weight percent (wt. %). Each of the protective coatingswas applied as about 50 micron (about 2 mils) coatings on aluminumpanels. The panels were placed on a conveyor belt moving at about 1.5m/min (about 5 feet/min) and were cured by exposure to a 600 watt/inchFusion V bulb followed by exposure to a 600 watt/inch Fusion H bulb. Thepanels were exposed to a total UV energy of 6.7 J/cm² UVA energy, 4.9J/cm² UVB energy, and 0.67 J/cm² UVC energy.

Example 1 wt. % Hybricor 204 38.10 Airex 900 0.22 Disperbyk 111 1.89 SR506D 8.53 CN991 21.51 Photomer 6892 10.48 Sanduvor 3068 0.24 Sanduvor3206 0.35 Ti-Pure R960 1.46 Syloid Rad 2005 2.33 Black 97076 1.07 SR3954.95 PI 191 3.78 Allyl cinnamate 1.09 SR 324 1.09 SR 257 1.09 Ebecryl170 1.82 100.00Airex 900 is a defoamer available from Tego Chemie Service GmbH ofEssen, Germany. Disperbyk® is a wetting agent available from BYK-Chemieof Wesel, Germany. Black 97076 is a pigment dispersion available fromLight Curable Coatings of Valley View, Ohio. PI 191 is a liquidphotoinitiator concentrate available from Light Curable Coatings.Ebecryl 170 is an adhesion promoter acrylate available from SurfaceSpecialties, formerly of UCB Chemicals of Brussels, Belgium, now ofCytec Industries of West Patterson, N.J.

Example 2 wt. % ELM-136-52 57.24 Airex 900 0.57 Photomer 6230 11.45Sanduvor 3068 0.35 Sanduvor 3206 0.35 Ti-Pure R960 2.29 Syloid Rad 20052.13 Black 97076 1.806 Blue G49UV15 0.022 Red G19UV57 0.002 SR395 12.32PI 130 4.56 Allyl Cinnamate 1.54 SR 324 1.54 SR 257 1.54 Ebecryl 1702.29 100.0ELM-136-52 is a 67% dispersion of Rhett P3 in CN991, available fromDeft, Inc. of Irvine, Calif. Blue G49UV15 and Red G19UV57 are pigmentdispersions available from Sun Chemical Corp. of Parsippany, N.J. PI 130is a liquid photoinitiator concentrate available from Light CurableCoatings.

Example 3 wt. % ELM-136-52 52.97 Airex 900 0.53 Poly bd R20LM 2.65CN966J75 14.20 Ti-Pure R960 7.94 Syloid ED-30 2.12 S-381-N5 1.05 Talc399 2.12 SR506D 10.59 PI 191 4.24 Ebecryl 170 1.59 100.00

S-381-N5 is a filler wax with good UV resistance available from ShamrockTechnologies, Inc. of Newark, N.J. and Talc 399 is a filler availablefrom Mineral and Pigment Solutions, Inc. of South Plainfield, N.J.

wt. % Example 4 ELM-136-52 52.63 Airex 900 0.53 Polybd R20LM 2.63CN966J75 14.11 Ti-Pure R960 7.90 Syloid ED-30 2.10 S-381-N5 1.05 Talc399 2.10 SR492 11.16 PI 191 4.21 Ebecryl 170 1.58 100.00 Example 5ELM-136-52 52.97 Airex 900 0.53 Poly bd R20LM 2.65 CN966J75 14.20Ti-Pure R960 7.94 Syloid ED-30 2.12 S-381-N5 1.05 Talc 399 2.12Pentaerythritol allyl ether 10.59 PI 191 4.24 Ebecryl 170 1.59 100.00Example 6 ELM-136-48 58.72 Airex 900 0.59 Tioxide TR93 1.76 Syloid ED-302.35 S-381-N5 0.86 Talc 399 2.35 Black 97076 0.59 Pentaerythritol allylether 5.63 Dipropylene glycol allyl 4.70 ether methacrylate PI 191 3.52Octa-Soligen 69HS 1.56 Allyl cinnamate 2.11 Roskydal UA VP LS 2396 13.85Clear Catalyst 11 1.41 100.00All components were mixed, with the Roskydal UA VP LS 2396 and the ClearCatalyst 11 added last. The coating was immediately applied after theRoskydal UA VP LS 2396 and the Clear Catalyst 11 were added. ELM-136-48is a 62.4% dispersion of Rhett P3 in CN991, available from Deft, Inc. ofIrvine, Calif. Octa-Soligen® 69HS is a drier activator available fromBorchers USA of Pittsburgh, Pa.

Accordingly, various exemplary embodiments of a corrosion-resistant,chromium-free, self-priming coating that is curable by ultraviolet lighthave been described. The coatings do not contain chromium, which can betoxic and carcinogenic, and release minimal or no VOCs and HAPs. Thecoatings can be applied as single-application coatings that can be curedquickly by ultraviolet light, thus decreasing vehicle or aircraftoperational unavailability. In addition, the protective coatings can beused for military and commercial aircraft and spacecraft, marine shipapplications, automotive applications, and other vehicle and industrialapplications. While at least one exemplary embodiment has been presentedin the foregoing detailed description, it should be appreciated that avast number of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thedescribed embodiments in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments.It should be understood that various changes can be made in the functionand arrangement of elements without departing from the scope as setforth in the appended claims and the legal equivalents thereof.

1. A method for coating a surface, the method comprising the steps of:formulating a chromium-free, self-priming coating; applying thechromium-free, self-priming coating to the surface; and curing thechromium-free, self-priming coating with ultraviolet light.
 2. Themethod of claim 1, wherein the step of formulating a chromium-free,self-priming coating comprises the step of combining an oligomer, amonomer, a photoinitiator, and a corrosion inhibitor.
 3. The method ofclaim 2, wherein the step of combining an oligomer, a monomer, aphotoinitiator, and a corrosion inhibitor comprises the step ofcombining a monomer, a photoinitiator, and a corrosion inhibitor with anoligomer selected from the group consisting of acrylates, methacrylates,diacrylates, triacrylates, and polyacrylates.
 4. The method of claim 3,wherein the step of combining a monomer, a photoinitiator, and acorrosion inhibitor with an oligomer selected from the group consistingof acrylates, methacrylates, diacrylates, triacrylates, andpolyacrylates comprises the step of combining a monomer, aphotoinitiator, and a corrosion inhibitor with an oligomer selected fromthe group consisting of aliphatic polyether urethane acrylates,diacrylates, and triacrylates, and aliphatic polyester urethaneacrylates, diacrylates, and triacrylates.
 5. The method of claim 2,wherein the step of combining an oligomer, a monomer, a photoinitiator,and a corrosion inhibitor comprises the step of combining an oligomer, aphotoinitiator, and a corrosion inhibitor with a monomer selected fromthe group consisting of acrylates, methacrylates, diacrylates,triacrylates, polyacrylates, allyl compounds, vinyl ethers, vinylesters, vinyl carboxylic acids, vinyl carboxylic acid salts, vinylamides, unsaturated dicarboxylic acid, and derivates thereof.
 6. Themethod of claim 2, wherein the step of combining an oligomer, a monomer,a photoinitiator, and a corrosion inhibitor comprises the step ofcombining an oligomer, a monomer, and a corrosion inhibitor withbisacylphosphine oxide.
 7. The method of claim 2, wherein the step ofcombining an oligomer, a monomer, a photoinitiator, and a corrosioninhibitor comprises the step of combining an oligomer, a monomer, aphotoinitiator, a corrosion inhibitor, and one or more compounds thatprovide a mechanism for curing the chromium-free, self-priming coatingwithout the use of ultraviolet light.
 8. The method of claim 7, whereinthe step of combining an oligomer, a monomer, a photoinitiator, acorrosion inhibitor, and one or more compounds that provide a mechanismfor curing the chromium-free, self-priming coating without the use ofultraviolet light comprises the step of combining an oligomer, amonomer, a photoinitiator, a corrosion inhibitor, and a peroxide.
 9. Themethod of claim 1, wherein the step of curing the chromium-free,self-priming coating with ultraviolet light comprises the step ofexposing the chromium-free, self-priming coating to ultraviolet lightprovided by a Fusion H bulb, a Fusion D bulb, a Fusion Q bulb, a FusionV bulb, or a combination thereof.
 10. The method of claim 9, wherein thestep of exposing the chromium-free, self-priming coating to theultraviolet light provided by a Fusion H bulb, a Fusion D bulb, a FusionQ bulb, a Fusion V bulb or a combination thereof comprises the step ofexposing the chromium-free, self-priming coating to the ultravioletlight provided by one of a Fusion V bulb and a Fusion H bulb followed byexposing the chromium-free, self-priming coating to the ultravioletlight provided by the other of the Fusion V bulb and the Fusion H. 11.The method of claim 1, wherein the step of formulating a chromium-free,self-priming coating comprises formulating the chromium-free,self-priming coating in multiple parts that are combined together beforethe step of applying the chromium-free, self-priming coating to thesurface.
 12. A coating for a surface, the coating comprising: anacrylated oligomer selected from the group consisting of acrylates,methacrylates, diacrylates, triacrylates, and polyacrylates; a monomerselected from the group consisting of acrylates, methacrylates,diacrylates, triacrylates, polyacrylates, allyl compounds, vinyl ethers,vinyl esters, vinyl carboxylic acids, vinyl carboxylic acid salts, vinylamides, unsaturated dicarboxylic acids, and derivatives thereof, aphotoinitiator; and a chromium-free corrosion inhibitor.
 13. The coatingof claim 12, wherein the acrylated oligomer is selected from the groupconsisting of aliphatic polyether urethane acrylates, diacrylates,triacrylates, and polyacrylates; aliphatic polyester urethane acrylates,diacrylates, triacrylates, and polyacrylates; aromatic polyetherurethane acrylates, diacrylates, triacrylates, and polyacrylates;aromatic polyester urethane acrylates, diacrylates, triacrylates, andpolyacrylates; polyester acrylates, diacrylates, triacrylates, andpolyacrylates; polyether acrylates, diacrylates, triacrylates, andpolyacrylates; epoxy acrylates, diacrylates, triacrylates, andpolyacrylates; polyamine acrylates, diacrylates, triacrylates, andpolyacrylates; and acrylated acrylic oligomers.
 14. The coating of claim13, wherein the acrylated oligomer is selected from the group consistingof aliphatic polyether urethane acrylates, diacrylates, andtriacrylates, and aliphatic polyester urethane acrylates, diacrylates,and triacrylates.
 15. The coating of claim 12, wherein thephotoinitiator is an acylphosphine oxide.
 16. The coating of claim 12,further comprising one or more compounds that impart a mechanism to curethe coating without ultraviolet light.
 17. A method for coating asurface, the method comprising the steps of: combining to form a singlemixture: an acrylated oligomer selected from the group consisting ofacrylates, methacrylates, diacrylates, triacrylates, and otherpolyacrylates; a monomer selected from the group consisting ofacrylates, methacrylates, diacrylates, triacrylates, polyacrylates,allyl compounds, vinyl ethers, vinyl esters, vinyl carboxylic acids,vinyl carboxylic acid salts, vinyl amides, unsaturated dicarboxylicacids, and derivatives thereof, a photoinitiator; a chromium-freecorrosion inhibitor; and a pigment; applying the mixture to the surface;and exposing the mixture to ultraviolet light.
 18. The method of claim17, wherein the step of combining to form a single mixture comprises thestep of combining to form a single mixture an oligomer selected from thegroup consisting of aliphatic polyether urethane acrylates, diacrylates,and triacrylates and aliphatic polyester urethane acrylates,diacrylates, and triacrylates, a monomer selected from the groupconsisting of acrylates, methacrylates, diacrylates, triacrylates,polyacrylates, allyl compounds, vinyl ethers, vinyl esters, vinylcarboxylic acids, vinyl carboxylic acid salts, vinyl amides, unsaturateddicarboxylic acids, and derivatives thereof, a photoinitiator, achromium-free corrosion inhibitor, and a pigment.
 19. The method ofclaim 17, wherein the step of exposing the mixture to ultraviolet lightcomprises the step of exposing the mixture first to one of a Fusion Hbulb and a Fusion V bulb followed by exposing the mixture to the otherof Fusion H bulb and a Fusion V bulb.
 20. The method of claim 17,wherein the step of combining to form a single mixture comprises thestep of combining to form a single mixture an acrylated oligomerselected from the group consisting of acrylates, methacrylates,diacrylates, triacrylates, and other polyacrylates; a monomer selectedfrom the group consisting of acrylates, methacrylates, diacrylates,triacrylates, polyacrylates, allyl compounds, vinyl ethers, vinylesters, vinyl carboxylic acids, vinyl carboxylic acid salts, vinylamides, unsaturated dicarboxylic acids, and derivatives thereof, aphotoinitiator; a chromium-free corrosion inhibitor; a pigment, and oneor more components that cause the mixture to cure without exposure toultraviolet light.